Forcing the mighty Tesco to post a profits warning and then launch a strategic review of its UK business must rank as one of Justin King's finest achievements as the chief executive of Sainsbury's. However, the prospect of a Tesco regaining its focus now looms over Sainsbury's. Both retailers are capable of succeeding at the same time, but there is a significant overlap in potential customers and store locations. Tesco has pledged to spend £1bn on turning around its UK stores, which includes cutting prices and modernising supermarkets. Its new Price Promise scheme to match the price of branded and own-brand foods in Sainsbury's has already riled King.

The future of the CEO

Speculation that Justin King is ready for a new challenge will not go away. Sainsbury's has consistently denied that King is preparing to leave, but headhunters are thought to have been tasked with setting the groundwork for his potential exit. King started as the chief executive of Sainsbury's in 2004 and, even if the City rumours are wide of the market, he will not lead the retailer forever. Replacing King will be a challenge – he has transformed the company during his period in charge, even if shareholders would like profits to have grown faster. There are impressive internal candidates though, most notably Mike Coupe, the commercial director.

With British consumer incomes set to remain under pressure and therefore sales growth slowing for supermarkets, shareholders have upped their focus on returns. One of the main criticisms of Justin King's tenure is that profits have not grown at the pace of sales. This is slightly unfair given that King pledged to revive Sainsbury's with a "sales-led" recovery and the company is hamstrung compared with its rivals because it leases more of its stores, leaving it with a hefty rent bill. Nonetheless, Sainsbury's must think carefully about how much to spend on opening new stores across the country and explore the areas where its margins can be bolstered.

Online strategy

Sainsbury's is already the second biggest seller of food online behind Tesco, giving it a significant foothold in the fastest growing part of the grocery industry. Sales for Sainsbury's are up 20pc year-on-year and the retailer serves more than 190,000 customers every week. However, the company must decide the best strategy to develop its online proposition – such as the scale of click-and-collect points, whether to continue picking online orders within stores, and the opportunities to sell general merchandise over the internet. This is an area of opportunity for Sainsbury's, but the profitability of online grocery shopping remains in doubt.